A faster sin() lookup function.

Development Libraries
7

Added the interpolation

float isin(float f)
{
  boolean pos = true;  // positive
  if (f < 0) 
  {
    f = -f;
    pos = !pos;  
  }  
  
  long x = f;
  unsigned int r = (f-x) * 256;
  
  if (x >= 360) x %= 360;
  if (x >= 180) 
  {
    x -= 180;
    pos = !pos;
  }
  if (x >= 90)
  {
    x = 180 - x;
    if (r != 0)
    {
      r = 256-r;
      x--;
    }
  }

  unsigned int v = isinTable16[x];
  // interpolate if needed
  if (r > 0) v = v + ((isinTable16[x+1] - v)/8 * r) /32;

  if (pos) return v * 0.0000152590219; // = /65535.0
  return v * -0.0000152590219 ;
}

runtime 45 micros (49 if the interpolation is not conditional) factor 2.6 faster than sine

steps of 0.1 degree
max error: 0.00015676 (factor 55.7 lower than without interpolation
avg error: 0.00004814 (factor 57.7 lower than without interpolation